Revenue Earning Equipment (Details Textuals) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010	Dec. 31, 2010
Revenue Earning Equipment (Textuals) [Abstract]
Cost	$ 8,214,943,000		$ 8,214,943,000		$ 7,448,618,000
Accumulated Depreciation	3,387,027,000		3,387,027,000		3,247,400,000
Effect of change in estimated residual values of revenue earning equipment on pre tax earnings	1,400,000		4,100,000
Accelerated depreciation	100,000	1,500,000	200,000	5,000,000
Assets Held under Capital Leases [Member]
Revenue Earning Equipment (Textuals) [Abstract]
Cost	24,700,000		24,700,000		29,200,000
Accumulated Depreciation	$ 15,200,000		$ 15,200,000		$ 18,500,000